1. Field of the Invention
The present invention relates to an encoding and recording apparatus, a playback apparatus and a program which can solve the possibility of a capacity shortage of a storage medium at the time of utilizing arbitrary content such as e-Book, music, and moving picture.
2. Description of the Related Art
In recent years, accompanying the development of an information-oriented society, a content distribution system by which content in which books, newspapers, music, moving pictures or the like are digitized (hereinafter, simply called content) are distributed to user terminals, and the content can be browsed has been broadly used.
However, because digitized content can be easily duplicated, an illegal act that the copyright of content is ignored is easily brought about. From the standpoint of preventing such an illegal act, a recording/playback system in which digitized content are encoded to record, and are decoded at the time of playback is usually used.
FIG. 43 is a schematic diagram showing a configuration of a secure storage medium and a playback apparatus for explanation of such a recording/playback system. A secure storage medium 10 has a system area 11, a protected area 12, and a user area 13.
The system area 11 is an area of which only a regular playback apparatus 20 can read out a medium identifier IDm, and has stored therein a medium identifier IDm which is identification information peculiar to a medium.
The protected area 12 is an area of which a general user cannot read out data directly, and has stored therein an encoded content key Enc_k(Kcn, IDm) formed due to a content key Kcn being encoded by a medium identifier IDm is stored.
The user area 13 is an area of which a general user can read out data directly, and has stored therein encoded content data Enc_c(Ctn, Kcn) formed due to content data Ctn being encoded by a content key Kcn.
With respect to the secure storage medium 10 as described above, the playback apparatus 20 operates as follows. Namely, at the playback apparatus 20, after an equipment authentication with the secure storage medium 10, a viewer unit 22 reads out a medium IDm of the system area 11 of the secure storage medium 10 via a read unit 21, and reads out an encoded content key Enc_k(Kcm, IDm) of the protected area 12 of the secure storage medium 10.
Next, at the viewer unit 22, a decoding unit Dec_k decodes the encoded content key Enc_k(Kcn, IDm) on the basis of the medium identifier IDm, and obtains a content key Kcn.
Thereafter, at the viewer unit 22, the encoded content data Enc_c(Ctn, Kcn) read out of the user area 13 of the secure storage medium 10 via the read unit 21 is encoded on the basis of this content key Kcn, and the obtained content data Ctn is displayed by a display processing unit 23.
Note that, related prior arts other than FIG. 43 are disclosed in “Content Protection for Recordable Media Specification SD Memory Card Book, Common Part”, <URL: http://www.4Centity.com>.
In a recording/playback system as described above, however, there is no problem usually. However, in accordance with the examination of the inventors, as will be described hereinafter, it can be thought that there is room for improvement because there is a possibility that the storage capacity of the protected area 12 is insufficient
Namely, the storage capacity of the protected area 12 of the secure storage medium 10 is, for example, in a case of an SD card, about 10 percents of the total capacity at the maximum.
On the other hand, an information amount of the content key Kcn has been increasing accompanying that a key length and attendant information are on the upward trend. In addition thereto, the number of content keys Kcn will increase in proportion to the number of content data Ctn to be recorded.
Accordingly, the possibility that the storage capacity of the protected area 12 of the secure storage medium 12 is coming to be insufficient due to an increase in the information amount of the content keys Kcn themselves and an increase in the number of the content keys Kcn can be thought of.
An object of the present invention is to provide an encoding and recording apparatus, a playback apparatus, and a program which can solve the possibility of a capacity shortage of a protected area accompanying an increase in an information amount and the number of content keys.